In breeding of plants cultivated for their seeds (also called seed crops) for example rice, wheat, barley, corn, soybean, canola, sunflower, millet and safflower, a major goal is to find genotypes that have a high seed yield. Breeders often have to analyse the seed yield of large populations of plants with different genotypes, obtained for example through sexual crossing of parental lines. Molecular breeders, who create variability by insertion of transgenes in a plant species, also have to cope with large plant populations of which the seed yield needs to be assessed. Tools for fast, accurate and efficient measurement of seed yield are a necessity for the plant breeding industry.
Plant phenotyping starts in essence with the creation of genotypic variation among plants of a given species. Following the creation of genotypic variation, selection of those genotypes having the most desirable agronomic phenotypes is performed. For example, plants may be selected for certain reproductive features such as: inflorescence number, size, or architecture, number of seeds per inflorescence, seed size, seed number, and seed weight. Such features contribute to the final seed yield and are called “yield components”. Traditional methods for evaluating yield components involve labour-intensive procedures such as manual and visual measurements of dimensions, counting of plant parts, and weighing of plant parts such as individual inflorescences and seeds. Usually, these operations require detaching the plant parts of interest from the subtending plant organs.
It is one practice to evaluate seed produced by plants by a procedure which involves several steps. The seeds are physically separated from the plant, the harvest step, and then cleaned to remove non-seed remnants originating from the maternal plant and dust or other contaminating particles. Mature seeds are discriminated from improperly matured seeds (hereinafter “immature seeds”), e.g. seeds that are not completely filled. In most cases the ratio of mature seeds versus immature seeds is recorded as a parameter that is relevant for the breeders. The mature seeds are weighed and counted, so that the total mature seed weight which is an important parameter for breeders, can be derived as well as the average weight per mature seed which gives a value for comparison with for example, the thousand kernel weight that is commonly used as an important parameter by breeders.
For example in rice plant phenotyping, it is common practice to measure seed yield by harvesting the mature panicles or seed bearing plant inflorescences at the end of the experiment of growing a plant. The panicles/inflorescences are then threshed and all the seeds are collected and counted. The seeds are usually covered by a dry outer covering, the husk. The filled husks (herein also named filled florets) can be separated from the empty ones using an air-blowing device. The empty husks can be discarded and the remaining fraction can be counted again. The filled husks can be weighed on an analytical balance. The total number of seeds is then determined by counting the number of filled husks that remained after the separation step. The total seed weight is measured by weighing all filled husks harvested from a plant. The total number of seeds (or florets) per plant can be determined by counting the number of husks (whether filled or not) harvested from a plant. Thousand Kernel Weight (TKW) can be extrapolated from the number of seeds counted and their total weight. The number of flowers per panicle can be calculated as being the ratio between the total number of seeds over the number of mature primary panicles. And the “seed fill ratio” or “seed filling ratio” can be calculated as being the proportion (expressed as a %) of the number of filled seeds (i.e. florets containing seeds) over the total number of seeds (i.e. total number of florets). In other words, the seed filling ratio is the percentage of florets that are filled with seed.
This manual seed harvesting and subsequent analysis steps are a very time and cost involving process.
Instruments used for conducting these measurements in such a procedure include balances for measuring seed weight and seed counters for counting the number of seeds, all of which exist in different commercially available types. One type of seed counter comprises an inlet for a batch of seed, a system that allows the seeds to drop one by one, and a system to detect each particle of a defined size that passes in front of an optical detector. Instruments for cleaning the seeds also exist in different commercially available types. Some are based on the passage of seeds over sets of shaking sieves with different mesh size, until seeds of the right particle size are retained on one of those sieves. Other instruments are based on the differential aerodynamic and/or gravity properties of seeds versus contaminants in a fluid flow, usually a stream of air. Discrimination of matured versus immature seeds can also be done based on the principle of differential aerodynamic/gravity properties.
EP1431744 describes an improved apparatus for the determining and recording characteristics of seed in a batch of plant product.
Another way of determining characteristics of seed in a batch of plant product can be found in EP1332354 which describes using spectral data signals to determine whether a seed exhibit a specific trait.
Disadvantages related to above referred methods and instruments is that they require a step of physically separating the seeds from the rest of the plant, which is time consuming and thereby also losing information on traits which might enable breeders to gain more insights in flowering and seed forming mechanisms of the crops under evaluation.
In 2009, Gray et al. developed a new method for estimating seed production of plants (Gray et al., 2009 New technology for estimating seed production of moist-soil plants. Journal of Wildlife Management 73:1229-1232) and recommended to use desktop scanners to predict seed yield of a press-dried panicle. This method does not permit to work in a high throughput manner as it needs manual handling before the analysis can start.